Monks can gain the monastery weapons feat.
it says: "You can use melee monk weapons with any of your monk feats or monk abilities that normally require unarmed attacks, though not if the feat or ability requires you to use a single specific type of attack, such as Crane Stance"
and the powerful fist class ability has:
"You know how to wield your fists as deadly weapons. The damage die for your fist changes to 1d6 instead of 1d4."
Now the question is: Does the feat apply also to this ability?